This invention pertains to method and apparatus for treating blood. It pertains particularly to method and apparatus for use in treating blood bank and transfusion blood for the removal of leucocytes and platelets.
It has been well established that the platelets and leucocytes contained in blood stored in a blood bank, and transfusion blood, tend to aggregate during storage and form masses having diameters of up to about 160 microns. The transfusion of blood containing such aggregates causes physiological and pathological changes in the lungs and other tissues of the patient's body. In some instances these changes result in serious complications.
For example, the leucocytes that are introduced into a body repeatedly by multiple transfusions have a tendency to induce immunological complications. Also, in cases of depressed immunological capacity transfusion of leucocytes may produce a graft vs. host reaction.
Swank, U.S. Pat. Nos. 3,448,041 and 3,593,854 disclose method and apparatus for the selective removal of leucocyte and platelet aggregates by passing the stored blood through a filter comprising filamentous materials such as filamentous polyester resin, filamentous polyamide resin, filamentous polyacrylic resin, filamentous glass, cotton and the like. Passage of the blood through these materials at the time of transfusion removes the harmful aggregates substantially completely without harming the other blood constituents. The patient thus is spared the harmful effects which he otherwise would suffer.
The Swank process accordingly increases the efficiency with which the blood bank blood routine may be carried out, since it enables the practice of a procedure broadly comprising withdrawing blood from a donor and passing the blood through a plastic tube into a plastic bag or other container which contains sufficient anti-coagulant to prevent the blood in the bag from coagulating. Where the bag has a capacity of 500 ccs, the volume of anticoagulant is about 50 ccs. The anticoagulant is in a solution in an isotonic and buffered solution calculated to prevent damage to the blood cells. Formerly the anticoagulant used was acid-citrate-dextrose (anticoagulant citrate dextrose solution, United States Pharmocopoeia XIX, p. 33); more recently, citrate-phosphate-dextrose (anticoagulant citrate phosphate dextrose solution, United States Pharmocopoeia XIX, p. 34).
After storage, the blood is passed through the filamentous filter described in the Swank patents aforesaid and introduced into the patient. Successful transfusions can be accomplished in this manner even after long storage periods. Also, the filter may be employed to great advantage as an extracorporeal filter during open heart surgery.
In view of the foregoing, the concept has arisen of removing the platelets and leucocytes from the blood in the first instance, before storage, rather than after storage. This technique would give rise to two advantages:
First, since the platelets and leucocytes are removed before storage, they cannot aggregate during storage, thereby simplifying the transfusion routine.
In the second place, it has been found that the lysosomes of leucocytes and platelets contain lytic enzymes which are released from platelet and leucocyte aggregates. These enzymes have the capacity and property of adversely affecting cells and tissues, thereby deteriorating the quality of the blood to be transfused. (Reid S. Connell and Roy L. Swank: Pulmonary microembolism after blood transfusions; an electron microscopic study, Annals of Surgery, Vol. 177, p. 40, 1973; and R. S. Connell, R. L. Swank, and M. C. Webb: The development of pulmonary ultrastructural lesions during hemorrhagic shock. J. of Trauma, Vol. 15, p. 116, 1975.)
This desirable result, i.e. the removal of the leucocytes and platelets from the blood prior to storage, is difficult of achievement, however, because if it is attempted to remove the leucocytes and platelets from the raw blood by passing the blood through a filamentous filter of the class referred to above in the Swank patents, the blood clots in the filter, making the filtration impossible.
It accordingly is the general purpose of the present invention to provide method and apparatus for removing leucocytes and platelets from blood without coagulation of the blood, providing a blood product suitable for storage over long periods of time, and suitable for use in transfusions of all categories.
The foregoing and other objects of this invention are achieved by the provision of a method which relies for its success upon the discovery that the blood anticoagulant heparin may be adsorbed efficiently on the filamentous filter materials aforesaid while retaining its anticoagulant properties over a substantial period of time.
In its broad outline the hereindescribed blood treating process accordingly comprises passing blood through a heparin-coated mass of filamentous polyester resin, polyamide resin, polyacrylic resin, glass, steel, cotton or cellulose. Thereafter the anticoagulated blood is passed through a mass of the same filamentous materials, but in a substantially heparin-free condition, for removal of its content of leucocytes and platelets preliminary to blood bank storage and/or use in transfusions.
The apparatus employed for the treatment comprises a vessel having an inlet with means for connection to a source of untreated blood, an outlet with means for connection to a receiving vessel, and a packing comprising at least one filamentous material of the group listed above. Preferably the packing comprises an upstream portion comprising heparinized filamentous material and a downstream portion comprising filamentous packing material substantially free from heparin. The upstream heparinized portion anticoagulates the blood so that it does not coagulate while passing through the downstream unheparinized packing portion which removes leucocytes and platelets from the transfusion blood.